The present invention generally relates to radio air navigational systems and more particularly to the generation of pulse-type signals used for the transmission of range and bearing information. The invention is capable of use in a wide range of other applications but is primarily intended for the above purpose and is therefore described in that context.
Radio air navigational systems of the "TACAN/DME" type employ pulse generating and transmitting equipment in providing range and bearing information to airplanes. A system of this type is described in "Principles and Features of Tacan (Tactical Air Navigational System)," published by Federal Telephone and Radio Company in 1956. A transmitter is associated with a special directional antenna broadcasts radio frequency pulses which upon receipt by appropriate equipment provide bearing information to airplanes within a defined geographical area. Additionally, there is a receiver-transmitter combination (transponder) which provides range information when interrogated by pulses transmitted from airborne equipment. In most instances, the bearing pulse transmitter and transponder are ground based while the bearing receiver and range pulse transmitter are airborne. However, as obvious the ground based equipment may be airborne, thereby providing range and bearing information to an aircraft or more properly speaking, between aircraft.
From the brief description presented and as provided in more detail by the referenced publication, systems of this type depend upon the generation and formation of pulses of particular character and repetition rate to send and receive air navigational information. Prior art systems have used vacuum tube electronic equipment of conventional design in the production of these pulsed signals. Of course, the concomitant size, power requirements and reliability factors of vacuum tube systems have created a need for the development of solid state equipment capable of meeting system requirements in an improved manner.
In furtherance of this, systems have been developed for airborne navigational equipment using triggered devices such as SCR's, Shockley diodes and other similar components. Since the pulse forming networks must operate at considerably high power levels, the pulse shaping and forming circuits have been significantly dependent upon the load impedance and power supply voltages. Additionally, since the recovery time of available triggered devices is relatively long, it is necessary to employ a separate device for each pulse when sending out bursts of pulses necessary in airborne systems of current design. Moreover, systems of this type may be susceptible to severe reliability problems unless design caution in circuit redundancy, etc. is used. The transistorized pulse generator of the present invention overcomes these difficulties providing equipment wherein pulse generation and shaping is accomplished at low power levels relatively unaffected by load impedance variations. As a result, a more nearly ideal frequency spectrum for the transmitted pulses is achieved in addition to a system having enhanced reliability and size economy.
Therefore, it is an object of the present invention to provide an improved apparatus for transmitting pulse signals in an air navigational system.
Another object of the present invention is to provide apparatus for transmitting air navigational pulses having smaller physical size and enhanced reliability.
Yet another object of the present invention is to provide an air navigational pulse transmitter relatively unaffected by variances in load impedance and power supply voltage.
Still another object of the present invention is to provide an air navigational pulse transmitter substantially unaffected by increases in in pulse repetition rate.